1. Field of the Invention
The present invention relates to information reproduction apparatuses, and more particularly, to an information reproduction apparatus that reproduces information from a disc in which audio data is compressed and recorded such as an optical disc and a magneto-optical disc.
2. Description of the Background Art
A conventional information reproduction apparatus such as a magneto-optical disc apparatus reproduces audio data digital-recorded spirally on a disc at a constant linear velocity to write the same sequentially into a buffer memory. In parallel with the reproduction operation, the information reproduction apparatus provides audio by reading out data from the buffer memory at a rate lower than the data reproduction rate from the disc and applying D/A conversion to the read out data. Such an information reproduction apparatus is implemented so that, even if track jumping of the optical pickup (beam spot) occurs due to physical disturbance or the like, error output such as sound intermittence will not occur by utilizing the difference between the rate of reproducing data from a disc (data writing rate into a buffer memory) and the rate of reading out data from a buffer memory.
FIG. 5 is a graph showing the change in the amount of data in a buffer memory. If data having a compression ratio of 4 is written continuously into an empty memory, the memory will become full in 0.75 seconds. In this case, the memory will become empty in 3 seconds if only data readout is carried out continuously from the full state of the memory. When reading and writing are carried out in parallel, the memory will become full in 1 second.
In an information reproduction apparatus using the above-described buffer memory, no data is stored in the memory when reproduction of information from a disc is first initiated. By carrying out data writing and data reading to and from a memory simultaneously, the memory becomes full in 1 second. Then, data writing is suspended and only data reading is carried out. When an empty region is generated in the memory, data writing is immediately reinitiated, whereby data writing and reading are carried out in parallel. In such a manner, the data reading and writing operation is controlled so that the amount of data in the memory is approximately 100%, as shown in FIG. 5.
Control of a data reading and writing operation in a conventional information reproduction apparatus is set forth in the following. The current amount of data in the memory is detected when the reproduction sector (the position of pickup with respect to disc) comes to the target sector (the sector subsequent to the last sector already written into memory). If the memory is not full, data of the reproduction sector is stored into the memory and the target sector updated. If the memory is full, the reproduction sector is kicked back by a distance of one track. By repeating the above-described operation, the data amount in the memory is maintained at the level of substantially 100%.
Because a kick back of 1 track is carried out in the above-described conventional information reproduction apparatus, the amount of data written into the memory at one time is that of 1 sector. During one operation of writing data into the memory, a kick back of 1 track is carried out 3 times on the average. This means that a kick back must be carried out frequently, resulting in increase in consumed power. This will particularly reduce the life time of a battery in a battery-driven system. Furthermore, because current for kicking back must be supplied frequently, the load (work amount) of the control circuit is increased.